DMF is a commodity in the chemical industry, widely used as a solvent and as a reaction medium in the preparation of dyes.
One method for preparing DMF on a commercial scale is that in which dimethylamine and carbon monoxide are catalytically reacted, using an alkali metal methylate as the catalyst. This produces crude DMF, which must be refined to be commercially acceptable. Before this is done, it is customary to deactivate the catalyst before the crude DMF is fed to the refining train because its presence in the train causes decomposition of DMF product into DMA and formic acid, for obvious reasons an undesirable thing.
This deactivation is ordinarily done by adding water to the reaction mass just before it is fed to the refining train. This deactivates the catalyst, as shown by the following illustrative equation: ##STR1## where X is an alkali metal.
The alkali metal formate (I) which forms is insoluble in the reaction mass, precipitates and can be removed by filtration or centrifugation.
However, as can be seen from equation (2), this method of deactivating the catalyst exacts an economic penalty since some of the product DMF is consumed. This yield loss can amount to as much as 2%, by weight.
It has now been found that the alkali metal methylate catalyst can be deactivated without this disadvantage by bringing the reaction mass into contact with an alkyl formate at the end of the reaction. The alkyl formate can be added directly, or it can be generated in the reaction mass in situ.